Electromagnetically stirred sand castings

ABSTRACT

A casting system, mold, and method are disclosed for electromagnetically stirring sand castings. In an embodiment, the casting mold includes a mold body having a cavity therein, and a passageway fluidly connecting the cavity with an exterior of the mold body. The passageway allows for introduction of a molten metal into the cavity. The mold body further includes at least one induction coil embedded in a cope of the mold body; and at least one induction coil embedded in a drag of the mold body. The induction coils are configured to generate an electromagnetic field for stirring a molten metal casting while it solidifies inside the mold.

BACKGROUND OF THE INVENTION

The invention relates generally to electromagnetic stirring of metal castings. More particularly, the invention relates to a casting system, mold, and method for electromagnetically stirring sand castings.

Sand casting refers to a metal casting process that uses sand as the mold material. A binder such as, e.g., clay or resin, may be mixed with sand, and the mixture may be moistened. This produces an aggregate material having suitable strength and plasticity to form the mold. The sand material is packed around a pattern, and the pattern is subsequently removed, leaving a cavity in the mold.

In the casting process, molten metal is poured into the mold cavity through a gating system, and the molten metal is allowed to solidify in the mold. For large metal castings, such as steel components of, e.g., wind turbines, which may weigh upwards of 4,500 to 5,000 kg (about 10,000 to 11,000 pounds), the solidification process may take several days to a week or more. After the casting has cooled, it can be shaken out of the mold.

The lengthy cooling time associated with sand casting presents several challenges. Steel and other alloy castings may be susceptible to segregation of elements during the cooling process due to different reactions. The longer cooling takes, i.e., the longer the cycle time, the greater the risk of this occurring. Elemental segregation can produce defects in the resulting casting that weaken the structure. Shrinkage defects may also occur when feed metal is unavailable to compensate for shrinkage as the metal cools and solidifies. These may naturally concentrate in the thermal center of the casting, which may disproportionately weaken that area of the resulting casting.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides a mold including a mold body having a cavity therein; the mold body further including a passageway fluidly connecting the cavity with an exterior of the mold, wherein the passageway allows for introduction of a molten metal into the cavity; and at least one induction coil embedded in the cope, or top half, of the mold, and at least one induction coil embedded in the drag, or bottom half, of the mold.

A second aspect of the disclosure provides a casting system comprising a mold body and a molten metal introduced into the mold. The mold body may include: a cavity therein; a passageway fluidly connecting the cavity with an exterior of the mold body; and at least one fluid-cooled induction coil embedded in a cope of the mold body and at least one fluid-cooled induction coil embedded in a drag of the mold body. The at least one fluid-cooled induction coil may be embedded in a cope of the mold body, and the at least one fluid-cooled induction coil may be embedded in a drag of the mold body to generate an electromagnetic field for stirring the molten metal during solidification of the molten metal.

A third aspect of the disclosure provides a method including: preparing a metal for casting, the preparing including melting the metal; introducing the molten metal into a cavity within a mold body; and using at least one induction coil, applying an electromagnetic field to the molten metal during solidification of the molten metal in the mold.

These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic drawing of an electromagnetic stirring apparatus in accordance with an embodiment of the disclosure.

FIG. 2 shows a three-dimensional drawing of an electromagnetic stirring apparatus in accordance with an embodiment of the disclosure.

FIG. 3 shows a flow chart depicting a process according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, aspects of the invention provide a casting system and mold structure for producing metal castings, shown in FIGS. 1-2 as well as a method of casting, shown in FIG. 3.

Referring to FIG. 1, casting system 100 includes mold body 110. In an embodiment, mold body 110 may be made of sand, and my include resin as a binder. Other possible binders may include clay, oil, or sodium silicate, among other binders. Mold body 110 includes cavity 120 disposed therein, which may take a regular or irregular shape as appropriate to the three-dimensional shape of the desired casting. A gating or passageway 130 fluidly connects cavity 120 with an exterior 140 of mold body 110. Passageway 130 allows for the introduction of molten metal 125 into cavity 120. Metal 125 can be any metal, and may particularly be an alloy such as, e.g., steel, any ferrous metal, or any nonferrous, conductive metals.

With reference to FIG. 2, at least one induction coil 150 may be embedded in cope 155 of mold body 110, and at least one induction coil 160 may be embedded in drag 165 of mold body 110. Each induction coil 150, 160 is disposed about cavity 120 or a feature thereof. The number of coils 150, 160 applied can vary depending upon the specific geometries of cavity 120 and therefore metal 125. For example, if cavity 120 and metal 125 have a feature or features that require specific properties, an induction coil 150, 160 may be applied to each feature.

Induction coils 150, 160 are fluid-cooled. In some embodiments, the fluid may be water. More specifically, in some embodiments, deionized water may be used. In further embodiments, induction coils 150 and 160 are low-frequency induction coils, operating at a frequency of, e.g., about 20 Hz to about 10 kHz. Induction coils 150, 160 may further have a cross-sectional diameter of between about 5 and about 30 mm, and may have either a round or a rectangular cross sectional shape. In further embodiments, induction coils 150, 160 are made of copper, and coated with ceramic, providing improved heat resistance.

Referring back to FIG. 1, induction coils 150, 160 may be used to generate an electromagnetic field 170 which stirs metal 125 in cavity 120 as metal 125 solidifies. Stirring of metal 125 by electromagnetic field 170 serves to homogenize the cast structure, and thus minimizes the degrading effects of segregation in the metal 125 casting. Electromagnetic stirring further disperses any instances of shrinkage defects throughout the metal 125 casting, rather than allowing them to concentrate in the thermal center of the metal 125 casting. The resulting metal 125 casting demonstrates improved endurance limits for tramp elements. Further, metal 125 casting may have a finer grain structure, a reduction in the percentage of porosity, and improved mechanical properties as a result of the increased cooling rates. Faster cooling also decreases cycle time, increasing process efficiency.

Referring to FIG. 3, a method of casting is also provided. In step 51, metal is melted and prepared for casting. The metal prepared may be an alloy such as, e.g., steel. In step S2, the molten metal is introduced into a cavity in a mold. In one embodiment, the mold may include sand. In step S3, an electromagnetic field is generated and applied to the metal, stirring it while it solidifies within the mold. The electromagnetic field may be generated by at least one induction coil. In some embodiments, there may be at least one induction coil in each of the cope and the drag of the mold. In step S4, the metal is cooled in substantial part by fluid flowing through the induction coils, which act as a cooling element. The fluid may be water, or more specifically, deionized water. In step S5, the metal casting can be removed from the mold.

In this manner, electromagnetically stirred sand castings may be produced. As used herein, the terms “first,” “second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of “up to about 5,000 kg, or, more specifically, about 4,500 kg to about 5,000 kg,” is inclusive of the endpoints and all intermediate values of the ranges of “about 4,500 kg to about 5,000 kg,” etc.).

While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A mold comprising a mold body having a cavity therein, the mold body further comprising: a passageway fluidly connecting the cavity with an exterior of the mold body, wherein the passageway allows for introduction of a molten metal into the cavity, wherein the cavity has an irregular three-dimensional shape in the form of a turbine component; at least one induction coil embedded in a cope of the mold body; and at least one induction coil embedded in a drag of the mold body, wherein the at least one induction coil embedded in the cope of the mold body, and the at least one induction coil embedded in the drag of the mold body further include a round or a rectangular cross sectional shape, and a cross-sectional diameter of about 30 mm.
 2. The mold of claim 1, wherein the mold body further comprises sand.
 3. The mold of claim 1, wherein the molten metal further comprises one of steel, a ferrous metal, or a nonferrous, conductive metal.
 4. The mold of claim 1, wherein the at least one induction coil embedded in the cope of the mold body and the at least one induction coil embedded in the drag of the mold body are fluid-cooled.
 5. The mold of claim 4, wherein the cooling fluid further comprises deionized water.
 6. The mold of claim 1, wherein the at least one induction coil embedded in the cope of the mold body, and the at least one induction coil embedded in the drag of the mold body further include copper, wherein the copper is coated with a ceramic.
 7. The mold of claim 1, wherein the at least one induction coil embedded in the cope of the mold body and the at least one induction coil embedded in the drag of the mold body operate at a frequency of between about 20 Hz and about 10 kHz.
 8. The mold of claim 1, wherein the at least one induction coil embedded in the cope of the mold body and the at least one induction coil embedded in the drag of the mold body are configured to generate an electromagnetic field for stirring the molten metal during solidification of the molten metal.
 9. (canceled)
 10. A casting system comprising: a mold body including: a cavity therein, wherein the cavity has an irregular three-dimensional shape in the form of a turbine component; a passageway fluidly connecting the cavity with an exterior of the mold body, wherein the passageway allows for introduction of a molten metal into the cavity; and at least one fluid-cooled induction coil embedded in a cope of the mold body and at least one fluid-cooled induction coil embedded in a drag of the mold body, wherein the at least one fluid-cooled induction coil embedded in a cope of the mold body and the at least one fluid-cooled induction coil embedded in a drag of the mold body are configured to generate an electromagnetic field for stirring the molten metal during solidification of the molten metal, wherein the at least one induction coil embedded in the cope of the mold body, and the at least one induction coil embedded in the drag of the mold body further include a round or a rectangular cross sectional shape, and a cross-sectional diameter of about 30 mm.
 11. The casting system of claim 10, wherein the mold body further comprises sand.
 12. The casting system of claim 10, wherein the molten metal further comprises one of steel, a ferrous metal, or a nonferrous, conductive metal.
 13. The casting system of claim 10, wherein the at least one induction coil embedded in the cope of the mold body, and the at least one induction coil embedded in the drag of the mold body further include copper, wherein the copper is coated with a ceramic.
 14. The casting system of claim 10, wherein the cooling fluid further comprises deionized water.
 15. The casting system of claim 10, wherein the at least one induction coil embedded in the cope of the mold body and the at least one induction coil embedded in the drag of the mold body operate at a frequency of between about 20 Hz and about 10 kHz. 16-20. (canceled) 